With a baseball in his right hand and shower shoes on both feet, Derek Lowe sat in the visiting dugout at Yankee Stadium yesterday totally at peace.

A few months ago, the oft-pouting Lowe was defensively – almost pleadingly – asking reporters why people felt he was a “mental Gidget” when he didn’t win. But as he prepared for today’s huge regular-season start against the resurgent Jon Lieber, Lowe (14-11, 4.91) seemed in a totally different frame of mind.

On June 6, Lowe’s ERA was 6.55. It was 6.02 on July 4. But since July 20, he’s gone more than five innings in 10 straight starts (at least 61/3 in nine of those) and posted a 6-2 record in those games.

What’s happened?

“Confidence,” Boston pitching coach Dave Wallace replied.

Is it that important? Is it that simple?

“Sure it is,” Wallace said.

Boston GM Theo Epstein has seen a different pitcher since the second half, but it’s one who’s appeared before. Don’t forget, Lowe tossed a no-hitter and won 21 games in 2002.

“The improved stuff, improved command, improved mound presence – he’s better in all facets in the game,” Epstein said. “He’s shown us that he can be an elite pitcher for long stretches.

“He’s already turned his season around. He’s worked hard at it, too.”

Lowe’s had a bad reputation of pulling some Jeff Weaver-esque facial contortions when things don’t go his way on the mound, something Epstein was speaking of when he mentioned mound presence.

“Different pitchers have different ways of expressing themselves on the mound,” Epstein said. “Everyone gives Derek a hard time when he shows some emotion on the mound, but that doesn’t mean he’s not confident.

“He’s pitching with a lot of confidence.”

A few months ago, this looked to be a real bowser of a pitching matchup. But even though Lieber (11-8, 4.46) had a bad outing in Baltimore in his last start, the Yankees are 15-9 in his starts.

“He’s more than held up,” manager Joe Torre said.

Boston first baseman Kevin Millar actually compared Lowe’s recent tempo to that of Lieber, so if both pitchers are on, expect a fast-paced game.

“Derek Lowe, when he was struggling in May and June, I said this guy will be around 17 wins,” Millar said. “And he right now has a chance to win 17 games …

“It’s the confidence factor. When he gets the ball, boom, boom, boom. He gets the ball and throws.

“When you start seeing them start rubbing the ball a little bit and thinking too much, I think that’s when you can see [struggles]. As a player, you try to eliminate all of the thought process when you’re competing.”